Fix gcc/g++ >= 7 and Apple LLVM >= 9 builds

Summary: gcc/g++ >= 7 and Apple LLVM >= 9 builds failed because of missing includes.

Reviewed By: andresy

Differential Revision: D13545106

fbshipit-source-id: aa2bb67e8484ab85fb7801e18de0d4449fbdcf85

Author: jacobkahn

flashlight/dataset/Dataset.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <cstring>
+#include <functional>
 #include <memory>
 #include <vector>
 

tests/nn/ModuleTest.cpp

@@ -5,6 +5,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <array>
+
 #include <gtest/gtest.h>
 
 #include <flashlight/autograd/autograd.h>